Recombinant DNA and related techniques have been used to study the molecular biology of the cytochromes P-450 (P-450s), a family of enzymes central to the activation and detoxification of carcinogens and to the metabolism of xenobiotics and drugs. The goal is to understand the structure and regulation of P-450 genes, to elucidate the molecular basis for the multiplicity of the P-450s and for the structural-functional relationships among them, and to determine the extent to which individual susceptibility of humans to cancer depends on the regulation of expression of specific P-450s. This year we have further characterized the P-450-M gene, further elucidating the finding that this gene is interdigitated with another independently regulated gene whose gene product is immunologically unrelated to P-450-M. We have used cloned cDNAs to P-450-BNF-B and P-450-ISI-G to show that the mRNAs for the P-450s have unique and common regions and to show that these mRNAs are regulated independently. We have continued our efforts to isolate the complete P-450-BNF-B and P-450-ISI-G genes.